Johan said that the server does not identify players, that's why inventory is not saved between logouts/logins. I dunno what's the thing with chests, probably similar.
happens to me once in a while, also with rainbow colors.
You just have to kill all animals on the map then they will respawn. There is a hard limit of animals on the map. If there are only 2-4 left, they will respawn. I don't know anything about despawning.
HTC Desire S/Android 2.3.7, happened once. I had two steaks then added them to furnace, then I still had two steaks. I added them once more, and finally I got nothing in inventory, and 4 steaks in furnace.
I will try to kill some zombies and make screenshots with the uncollectable feather, but it is very hard to me to find one from a zombie, so really don't know, it's sad.
It may be connected with a world renderer annoyance - world like 256x256 should not have much water, instead more land (it will be easier to find mushrooms, cacti etc if there will be more land). So if you somehow got a world with extreme lot of water then they will spawn on woter. But it's only my thoughts. and i noticed it too. diving just to get my food...